In a flip-chip assembly, the coefficient of thermal expansion (CTE) mismatch between a flip-chip die and a substrate, which may result in cracks in solder joints, is a major contributor of reliability concerns. To address this issue, mold compounds are widely used to underfill the flip-chip die. By underfilling the flip-chip die, the mold compounds fill the space between the flip-chip die and the substrate, and encapsulate the solder joints. These mold compounds provide mechanical support to the solder joints. However, presence of the underfill materials between the flip-chip die and the substrate may adversely impact the electronic performance of the flip-chip die, especially for high-frequency flip-chip die.
Accordingly, there remains a need for improved packaging methods to maintain superior electronic performance of the flip-chip die without sacrificing the reliability of the flip-chip die due to cracks in the solder joints. In addition, to accommodate the increased demand of portable communication devices, there is also a strong need to reduce the size of the final semiconductor package.